The patterns of breathing change across states--presumably because of changing inputs to brainstem respiratory neurons. These inputs include those for behavioral control in wakefulness-and possibly in rapid eye movement sleep--, and they may increase or decrease respiration. Little is known of the interaction of these afferents with brainstem respiratory neurons. Proposed herein are tests of a hypothesis about the integration of state-related afferents within the respiratory system. This hypothesis proposes that state-related afferents engage a class of respiratory cell that acts as an interface between afferents having nonrespiratory forms and the respiratory cells of the oscillator. These cells of the interface, it is proposed, have respiratory activity that is weakened and distorted by nonrespiratory inputs that change in different states. In contract, other respiratory cells, putatively those of the oscillator, have strong and consistent respiratory activity, are unresponsive to nonrespiratory inputs and less affected by changed in state. The mode of interaction of the cells of the interface with the cells of the oscillator is unknown. It is assumed, however, that a subset of the former is activated to inhibit the latter when breathing is stopped behaviorally. To test these ideas, the activity of respiratory neurons will be recorded in the medullary and pontine respiratory groups during sleep and wakefulness, during behavioral control of breathing, and in response to sensory stimuli. These studies of intact, unanesthetized animals are significant for understanding behavioral control of breathing, breathing in sleep, integration of nonrespiratory afferents within the respiratory system, and the nature of the respiratory oscillator.